Constraints and Catalysts in Cerebellar Evolution

Abstract

The cerebellum comprises a remarkably stereotyped neural circuit, elements of which, such as the granule cell‐Purkinje cell synapse, are highly conserved across vertebrates. It functions as an adaptive filter that can be employed in regulating feed forward control of movement, but has a wider range of functions including in mammals, a demonstrable role in cognitive development. The range of neural functions modulated by cerebellar activity is a product of its output connections. In many species these are mediated by cerebellar nuclei whose number and projections vary systematically across major classes of vertebrates. Notably, the connection of cerebellar nuclei to the thalamus and hence the ability of the cerebellum to participate in forebrain activity is a mammalian innovation. Cerebellum size is also a key adaptive variable amongst different species with some species of both fish and mammals displaying relatively large, elaborately foliated cerebellum. Different strategies for generating large numbers of cells are adopted by different classes of vertebrates. In particular, the appearance of a transient, external granule cell layer (EGL) in cerebellar development is a tetrapod innovation. In some reptiles, birds and mammals, the EGL becomes a proliferative layer, which leads to a rapid clonal expansion of granule cells and the potential for foliation. Both the diversification of connectivity (cerebellar nuclei) and transit amplification (in the EGL) are adaptive properties within derivatives of a single defined pool of progenitors at the embryonic “rhombic lip”. Different derivatives are generated within distinct cohorts. Within these cohorts the heterochronic shift in the expression of a small number of genes appears to be responsible for generating the key changes in cerebellar development in vertebrates.Support or Funding InformationMedical Research Council, UKBBSRCThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.